In the course of concealing the presence of safety air bags in a motor vehicles there has evolved a cover made of plastic material that normally conceals the air bag and has a hidden or invisible tear seam that is torn or ruptured by the stress of air bag inflation to form an opening for deployment of the air bag into the passenger compartment. There are also cover assemblies wherein the cover is ruptured by piercing devices to form an opening therethrough for air bag deployment. Examples of such air bag concealing cover devices are disclosed in U.S. Pat. Nos. 5,072,967; 5,154,444 and 5,256,354 assigned to the assignee of this invention. While these concealing cover devices have proven generally satisfactory, most plastic materials tend to become embrittled at very low ambient temperatures. As a results such covers might fragment along the edges of the opening in the cover produced by the rupture when the air bag is required to deploy at extremely cold temperatures such as -20 degrees Fahrenheit and below. Consequently, there is only a limited number of materials suitable for this use.
It is known to incorporate various heater devices in association with an air bag concealing cover arrangement. But they have been for the purpose of producing (burning) the opening through the plastic cover for air bag deployment at the time of impact and are not suited to assuring against fragmentation of the plastic material at that instant let alone in an energy efficient manner. Examples of such heater devices are disclosed in U.S. Pat. Nos. 5,080,393 and 5,217,244.